feat(rss): generate rss feed from podcast entity

- refactor episode, podcast and category entities to add dynamic properties
- refactor Routes when adding feed route
- update migration files to better fit itunes' and rss' specs
- update podcast and episode forms
- add SimpleRSSElement class to Libraries
- add rss_helper
- update home controller to redirect if system has only one podcast

app/Controllers/BaseController.php

@@ -50,7 +50,7 @@ class BaseController extends Controller
         set_user_session_referer();
     }
 
-    protected function stats($postcast_id)
+    protected static function triggerWebpageHit($postcast_id)
     {
         webpage_hit($postcast_id);
     }